Radiation dispersing cavities

ABSTRACT

A radiation dispersing cavity has its interior surface covered by a plurality of deformations, each of which acts as a dispersing element which is small with respect to the effective diameter of the cavity and yet large with respect to the wavelengths processed by the integrating cavity. The interior surface of the cavity is coated with a material which provides the proper reflectivity for the wavelengths of interest. The interior of the cavity is covered with at least two different sets of interlocking deformations producing at least two different apparent planes of reflection. Use of alternating concave-inward, concave-outward deformations facilitates smooth transitions between deformations, preventing development of hot spots at sharp discontinuities.

The govenment has rights in this invention pursuant to Contract No.DASG60-79-C-0029 awarded by the Department of the Army.

This is a Continuation-In-Part of Ser. No. 481,164, filed Apr. 1,1983,now U.S. Pat. No. 4,551,628.

BACKGROUND OF THE INVENTION

This invention relates to radiation dispersing cavities. Moreparticularly, this invention relates to radiation dispersing cavitieswhich rely upon a large number of interlocking deformations to thesurface of the cavity to achieve a very close approximation to uniformLambertian mixing of the input radiation.

Basically, this invention has two major embodiments, one as an opticalintegrating cavity and one as a black body emitter. The opticalintegrating cavity will be discussed first. An integrating cavity can bedefined as a device which mixes radiation, whether polarized or Plankianor whatever, entering the cavity from different directions and emitsuniformly mixed Lambertian distributed radiation. In most of the priorart devices, the emission of the uniformly mixed radiation is along adirection orthogonal to the source or sources of radiation at the inputor inputs. The homogenized radiation is then dependent upon the sum ofthe spectral inputs and independent of any geometrical property of theinput optics.

Most integrating cavities are spherical in shape. The integratingspheres in the prior art which are used in the visible portion of thespectrum are normally made by "smoking" the inside of a spherical cavitywith magnesium oxide. The magnesium oxide is transparent to visibleradiation, and, in its non-absorbing spectral regime, light is partlyreflected from random facets at the outer surface of the magnesium oxidecoating, partly transmitted and suffers reflection and refraction ateach succeeding interface which it meets. Due to the random orientationof the porous magnesium oxide smoke and its low absorption, itrandomizes the directed input radiation into a random Lambertianradiation distribution. U.S. Pat. No. 4,309,746 to Rushworth illustratesthe employment of the magnesium oxide internal coating for theintegrating cavity in its recitation in column 5. Another common coatingemployed in the prior art integrating cavities is barium sulphate. Itsuse is demonstrated in U.S. Pat. No. 4,232,971 to Suga in its teachingat column 4. It is important to note that these prior art devices relyupon the properties of the coating material itself to randomize thereflected radiation within the integrating cavity. This should becontrasted with the fundamentally different mechanism employed in thepresent invention in which the conformation of the cavity surface withits interlocking deformations produces the randomizing effect throughthe interaction of the light in the cavity with the individualreflecting elements. Unfortunately, since these prior art devices relyupon the optical properties of the coating materials emplaced upon theinterior cavity surface, the effective bandwidth of the device islimited by the properties of the internal coating. Consequently, theintegrating cavity technology of the prior art has not been able to beextended satisfactorily out of the visible portion of the opticalspectrum, specifically not into the infrared bandwidths withsatisfactory results. One U.S. Patent in the prior art, U.S. Pat. No.3,319,071, to Werth et al., bears further comment. This referencedescribes the construction of a chamber used for measuring infraredabsorption characteristics of gases in which the chamber bears asuperficial resemblance to one embodiment of the integrating cavity ofthe present invention. However, the dimples which are formed in thesurface of the prior art chamber are specifically designed such that thereflections therefrom will produce specular, rather than diffuse,reflections within the sphere, as is taught at the bottom of column 2 ofthis reference.

SUMMARY OF THE INVENTION

The radiation dispersing cavity of this invention is for use in mixing abandwidth of radiation and comprises a cavity surface substantiallycovered by a plurality of interlocking deformations, each deformationbeing a surface of revolution whose axis is substantially normal to thecavity surface wherein the surface of revolution is formed by a conicsuch that a cross section containing the axis is a portion of the conicsubtending an arc of from 10° to about 140° measured from the focus ofthe conic and the arc has an effective diameter measured across the endpoints of the arc wherein the ratio of the longest wavelength in thebandwidth to the arc diameter of a deformation is less than one-fifthand wherein the diameter of the cavity is at least five times the arcdiameter of a deformation, wherein the cavity surface is characterizedby a specific reflectivity for the bandwidth of the radiation. Thecavity itself may be, but is not limited to, a sphere, an ellipsoid, ora cylinder and is covered with a coating of proper reflectivity foroperation upon the wavelengths of interest.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of the cavity wall with aray diagram showing incident and reflected light rays from thereflecting element;

FIG. 2 is a cross-sectional view of two larger portions of cavity wallsshowing in the left quadrant an embodiment with the reflecting elementsbeing concave inward and in the right quadrant showing reflectingelements which are convex inward;

FIG. 3 is a plan view of a portion of the cavity wall for an embodimentfor which the reflecting elements are spherical indentations;

FIG. 3A is a plan view of a portion of the cavity wall for an embodimenthaving two different sets of spherical deformations;

FIG. 4 is a cross-sectional view taken along section lines as indicatedin FIG. 3;

FIG. 4A is a cross-sectional view taken along section lines as indicatedin FIG. 3A showing alternating hills and valleys for the deformations;and

FIG. 5 is an isometric view of another embodiment of the invention inwhich the integrating cavity is in the form of a cylinder with itsreflecting elements being parallel cylindrical arcs incised into thecavity surface.

DETAILED DESCRIPTION OF THE INVENTION

The physical concepts behind the radiation dispersing cavities of thisinvention are applicable to several different embodiments. Oneembodiment takes the form of integrating cavities which are useful forproducing a random Lambertian radiation distribution from various inputradiation sources. Another embodiment takes the form of a black bodyemitter which produces an electromagnetic spectral output given byPlanck's radiation law which is a function only of the temperature ofthe black body emitter. Still another embodiment takes the form of whatmay be called a gray body emitter which is a combination of the abovetwo effects for the integrating cavity and black body emitter forms ofthe invention. Most forms of the integrating cavity embodiment of thisinvention will require a high reflectivity at the reflective surface ofthe cavity. Normally this will be produced by a gold or gold alloycoating deposited upon the interior of the cavity. However, in someapplications a silver coating or an aluminum coating may be sufficient.Additionally, if the cavity itself is fabricated from aluminum, it maybe possible in some applications to dispense with the need for a coatingand utilize the aluminum body material in a highly polished statedirectly. Although the majority of the following description will bedevoted to developing those embodiments of this invention which utilizedeformations which have a circular cross section, it should be realizedthat the cross section of these deformations is not necessarily limitedto circular cross sections. In the general case, the deformations may beformed by a surface of revolution which has as its axis a line which issubstantially normal to the interior surface of the dispersing cavity atthe point of the deformation. This surface may be spheric or aspheric.Finally, in the way of general remarks about such dispersing cavities,the input aperture size should have an effective aperture diameter whichis equal to at least the average effective diameter of the deformationsinside the cavity. Also the input beam angular divergence should coverat least about five deformation diameters in order to maximize theefficiency of the dispersion chamber.

In many systems, it is desirable to take radiation from a number ofdifferent sources and combine the radiation into a prescribed spectraldistribution. The spectral input can be from broad band and narrow bandfiltered black body sources, laser sources, spark discharge, glowdischarge, and other various sources which are brought together fromdifferent directions. The integrating cavity embodiment of thisinvention is uniquely able to be used as a mixing chamber for thesevarious sources of radiation and is useful over wide ranges ofwavelengths, especially in the infrared region.

The integrating cavity is independent of the wavelength of the inputradiation for all values of the ratio wavelength/d' for values less thanabout 0.20 where d' is the diameter of the deformation in the surface ofthe integrating cavity. While d' is the effective diameter of thecircular deformation measured at the surface, it should be rememberedthat d is a separate dimension which is equal to twice the radius ofcurvature of the circular cross-section deformation. Concurrently, theeffective diameter of the cavity must be greater than about five timesthe diameter of the deformations. When both of these conditions aresatisfied, the bandwidth of the integrating cavities is limited only bythe absorption properties of the specularly reflective film used to coatthe interior of the cavity.

Up to this point, the integrating cavities of this invention have beendiscussed in general terms. Specific configurations of the cavityinclude spheres, ellipsoids, and cylindrical cavities. The followingdiscussion will concentrate first on the integrating sphere.

The theory of operation for the integrating sphere embodiment, althoughthe theory holds true for the other embodiments as well, is that if theinside of a sphere having a radius, R, is covered with spherical concaveor convex deformations where the radius of curvature, r, is smallcompared to the radius of the integrating sphere, then each lens-likesurface can transform an incident plane wave of light into a divergentwave front filling almost 2 steradians. This effect is shown in FIG. 1,which portrays a cross-sectional view of the interior of the integratingsphere showing the sphere wall 25 in cross section and the circular arcAB which is the cross-sectional view of one of the sphericaldeformations in the integrating sphere. Point O is the center ofcurvature for the spherical deformation having a radius r. In thisparticular embodiment, the arc subtends an angle of 90° which for mostpurposes will be desirable since it will minimize the surface area ofthe integrating cavity while maximizing the solid angle into which theplane wave is reflected. FIG. 1 shows an incident plane wave front whichbisects the angle AOB. Since the angle AOB is a right angle, the rays 10thru 21 will be reflected as shown from the arcuate surface of thereflecting element into the reflected rays 10' through 21', with ray 10being reflected back upon itself and ray 21 being reflected as a rightangle and with the other rays reflecting at angles distributed uniformlybetween these two extremes. Similar geometric constructions for planewaves incident at both small and large angles demonstrate that thereflected wave fronts will spread over large solid angles approaching 2πsteradians. Such constructions of plane wave normals incident atincreasing angles to ray 10 show that the caustics of reflected raybundles translate towards the periphery of each indentation. Since theincident waves come from all directions, the reflected rays which exitfrom the output aperture will appear to emanate approximately uniformlyfrom all areas of each indentation.

A common objective for the use of an integrating cavity is to transformbroad band radiation directed into the input aperture of the cavity intonon-directional radiation exiting through the output aperture. Toachieve this, normally the integrating cavity must randomize theradiation so that it is unpolarized, and the flux density inside thecavity must be uniform in all directions. When this condition is met,the directional intensity of radiation which exits the aperture isdistributed according to the Lambertian cos² θ law. Interestingly, sincethe construction of the present invention so effectively scatters theincident light, there is no significant direct reflection from theopposite wall back through the inlet aperture, and hence no strictrequirement for a non-diametrical viewing direction or exit aperture asis found in the prior art of integrating cavities.

The integrating sphere of this embodiment accomplishes thisrandomization by dividing the interior surface of the integrating sphereinto a large number of short focal length spherical mirrors which arespaced such that no extended area of the original spherical surface ofthe sphere remains. Only sharp edges and points at the intersections ofthese spherical mirrors exist in addition to the short focal lengthcurved surfaces themselves, and these should have smaller convex radiiof curvature than the shortest wavelengths of interest. FIG. 2 shows twodifferent configurations for the spherical deformations in theintegrating sphere. In the left quadrant, the short focal length curvedsurfaces are convex inwards. The center of the integrating sphere isshown as point O, the cross-sectional view exposes the material in theintegrating sphere wall 25, the effective radius of the integratingsphere is R, and the distances to the centers of the arcs of therespective elements are R+r and R-r, respectively. Again, the radius ofcurvature of the individual spherical deformations is r. It isanticipated that the concave inwards embodiment would be easier tofabricate; however, either implementation is effective.

FIG. 3 shows in plan view the interlocking spherical deformations in thewall of the integrating cavity. The perimeters of each of thedeformations as they would intersect the original interior surface ofthe cavity are shown as the dotted lines 30. However, since theyinterlock, the actual boundaries between the elements will be marked bythe straight line segments 32 which form a honeycomb-like pattern ofinterlocking hexagons on the surface of the cavity. Note that thediscussion above requires that these straight line segments 32 and theirrespective intersections all have radii of curvature which are smallerthan the wavelengths of interest for the integrating cavity.

FIG. 4 shows a cross-sectional view of the plan view shown in FIG. 3.The cavity wall material 25 is shown in cross section along with thecorresponding arcuate segments 32' which correspond to the straight linesegments 32 in FIG. 3. The centers of curvature for the individualdeformations are shown as the crosses labelled O. Corresponding centersof curvatures for the elements which are out of the plane of section areshown by the dotted crosses. This discussion has assumed that thespherical deformations are all essentially identical in size. This isnot a requirement for the operability of the device. The onlyrequirement is that the diameter of the spherical elements as theydeform the surface is large with respect to the wavelengths involved.Hence, there could be two or more different sizes of deformations in thewall of the integrating cavity. For example, the points of intersectionof the arcuate lines 32 in FIG. 3 could serve as centers for a secondset of deformations having a smaller effective diameter than theoriginal deformations 30. Nevertheless, regardless of the size of thedeformations, they must interlock in arcuate lines and/or at points ofintersection.

Alternate embodiments of the concept introduced immediately above areshown in FIGS. 3A and 4A. The basic concept of utilizing different sizesof deformations, although somewhat more difficult to fabricate, permitsthe utilization of multiple apparent planes of reflection. For thepurposes of this discussion, an apparent plane of reflection is thatplane which contains the average depth points for a given set ofdeformation elements. The average depth point for a deformation isdefined herein as the midpoint between the most distal point in adeformation and the most proximate point, both relative to the center ofthe cavity, the midpoint being located on the axis of the surface ofrevolution which defines the deformation. Multiple apparent planes ofreflection in turn create more dispersion than would a single apparentplane of reflection and result in a dispersion of radiation that moreclosely approaches that of the ideal cos² θ distribution. The use of twodifferent sizes of deformations is shown in plan view in FIG. 3A.Whereas the embodiment shown in FIG. 3 produces an interlockinghexagonal intersection grid, the grid in FIG. 3A is made up ofinterlocking hexagons and equilateral triangles as shown. These hexagonscorrespond, for the specific embodiment shown, to the concave inwardslarger radius (r₁) deformations 60 (valleys) shown in the cross sectionview taken along section line 4A--4A shown in FIG. 4A. The trianglescorrespond to the tighter radius (r₂) convex inwards deformations 62(hills) also shown in FIG. 4A. This specific embodiment produces twoseparate apparent planes of reflection, one from the hills and one fromthe valleys. Addition of further sets of interlocking elements in asimilar fashion will produce additional apparent planes of reflection.FIGS. 3A and 4A also illustrate the concept of alternating interlockinghills and valleys in constructing the deformations. This concept isdesirable in that it produces relatively smoother transitions (64, 65and 66 in FIGS. 3A and 3B) at the interlocking intersections betweendeformations as opposed to the relatively sharp ridges produced whenonly valleys are used for deformations or the acute valleys formed atthe intersections between the hills-only construction, these effectsbeing illustrated respectively in the left and right quadrants of FIG.2.

One method of fabrication for the integrating sphere embodiment is tomachine a master integrating sphere on the inside surface of a sphericalcavity cut into several sections. The individual deformations would thenbe machined into the surface with continuity maintained across matingedges of the various sections of the sphere. Next, a silicone rubber orother flexible plastic mold which can be electrically conductive ornon-conductive is made of each half of the sphere. These negative moldsare then used for electroless and/or electrolytic plating of a largenumber of substantially identical integrating spheres. First areflective or absorbing coating such as gold is deposited and then abase structural metal such as copper is deposited until the wallthickness produces a mechanically stable structure. Another method wouldbe to use a solid form which is divided into eight equilateral sphericalright triangles as the plating mold sections. When finished, the moldwould slip out of the plated part without interference.

For general example, consider a one centimeter diameter integratingsphere with surface area of 4πR² =πcm². If an individual scatteringelement has an equivalent projected area of a one millimeter diameterplane circle, then the area of each element would be πr² =π/4 mm².Therefore, the inside of the sphere would contain about 400 suchelements. For the infrared five to 25 micron band, the ratio of thediameter of the element to the wavelength varies from 40 at 25 micronsto 200 at five microns. For these dimensions, the size of the sphericalreflecting elements will not contribute appreciably to wavelengthdependent phenomena. This should be contrasted to the prior art deviceswhich normally employ SiC scattering centers deposited on the insidesurface of the integrating cavity which are then overplated with asuitable high reflectivity material such as gold. In these prior artdevices, the scattering centers cannot be well controlled and give riseto these detrimental wavelength dependent phenomena.

In another example, a 50 millimeter diameter integrating sphere iscovered with 3 millimeter diameter spherical reflecting elements tocover the infrared band from five microns to 30 microns. The ratio ofthe element diameter to the largest wavelength (d/wavelength=100) showsthat no spectral effects should be observed. Performing a computationbased on the hexagonal geometry shown in FIG. 3, the number ofreflecting elements possible is given by ##EQU1##

For these dimensions, each reflecting element occupies a solid angle ofabout 9.4×10⁻³ sr (or 1.57° full cone angle) measured from the exit portof the integrating sphere. Since the number of reflecting elementsincreases inversely as the square of the radius, the number of elementscould be increased by a factor of 10 and still allow for ten wavelengthsacross each element for radiation at 30 microns.

A second embodiment of this invention is a cylindrical integratingcavity. Such cylindrical integrating cavities are useful in mixingradiation input into the cavity from a line source. One such cavity isshown in FIG. 5. The cylindrical cavity shell 54 is pierced by anentrance slit parallel to its long axis having an opening width markedby the numeral 50. A corresponding exit slit has its opening widthlabelled 51. However, it should be noted that the high efficiencydispersion characteristic of the interior surface does not necessarilyrequire separate entrance and exit slits; a single slit could sufficefor some usages. The cylinder is capped at each end by mirror end caps52, one of which has been removed to show the detailed construction ofthe interior of the cavity. In one version of this embodiment, theindividual reflecting elements take the form of cylindrical groovesincised into the cylinder walls, each of which has an individual radiusof curvature marked r. The radius of the cylindrical integrating cavityitself is R which represents the radius of the interior of the cavityprior to the formation of the individual cylindrical reflecting grooves.As before, these grooves need not be concave inwards as shown in thisfigure, but could be alternatively formed as convex inward lands. Inanother alternative, the grooves and lands can alternate. The axialcenter of the integrating cylinder is marked by the centerpoint labelledO. This particular version of the cylindrical integrating cavity isuseful in its employment in a larger system which comprises a singleline source coupled to the cylindrical integrating cavity by a waveguidein which it is desirable for the polarization of the waveguide polarizedradiation to be preserved. The waveguides coupling the single linesource and the integrating cavity produce polarized radiation with theelectric vector perpendicular to the plane faces of the waveguide. Theemployment of the long cylindrical grooves cut in the cylindricalintegrating cavity preserve the polarization of this radiation.Nevertheless, in situations where it is not necessary to preserve thispolarization, the spherical dimple version discussed in relationship tothe spherical integrating cavity above may be employed in the interiorof the cylindrical integrating cavity. This particular version is notshown.

Returning to a more general discussion, the integrating cavity isconstructed in accordance with this invention may be used in theultraviolet, visible, the near infrared, the far infrared, submillimeter and millimeter bands of electromagnetic spectrum to transformdirectional light sources of any spectral bandwidth into a path orhistory independent Lambertian output beam which is directlyproportional to the total energy in the beam. Similarly it can mix anumber of different spectral sources (broadband, band-limited andmonochromatic in any combination) into a new source in which the outputspectrum has a predetermined (preset) distribution. Also the integratingcavity may act as a near neutral density beam attenuating component byselection of a suitable coating material for the interior of theintegrating cavity with an appropriate reflectivity coefficient toproduce the desired attenuation.

As was stated above, the optimum arc for the individual reflectingelements to subtend is approximately 90° measured from the center ofcurvature of the arc. However, it is possible that this arc may fallanywhere in the range from about 10° at the minimum to about 140° at themaximum before inefficiencies overcome the construction. At the low end(10°) the deformation becomes so shallow that the dispersingcharacteristic of the reflectivity of the surface becomes too small anddirect reflections or glance begin to domonate. At the high end of therange (140°) internal reflections within each reflecting elementintroduce inefficiencies due to absorption effects from these multiplereflections from the coating material. Also, in some situations it maybe desirable to use an arc which is slightly less than 90° in situationsin which heat transfer effects at the sharp edges and ridges between theelements become important. These usages include measurements conductedin the infrared regions.

Another significant usage for the radiation dispersing cavity of thisinvention is in black body emitters. These devices are used to producean electromagnetic spectral output given by Planck's radiation law whichis a function only of temperature. The only significant physicaldifference between the optical integrating cavities discussed above andthe black body emitter is in the reflectivity of the interior surface orthe surface coating of the chamber. In the case of the integratingcavities, the reflectivity of the coating will normally be very high,although in some instances the integrating cavity may be employed eitheras a neutral density or spectral filter and will have a lowerreflectivity coating in order to partially attenuate the radiation as itreflects off the interior surfaces of the chamber. However, the blackbody emitter depends for its functioning upon a very low reflectivitysurface or surface coating, since the object is to have a very highabsorption at the chamber surface rather than high reflectivity as isthe case in the integrating cavities except that the black body cavityis heated to some controlled temperature and the integrating cavity iscooled to prevent it from adding energy into the spectral band ofinterest. The actual geometric construction of the black body emitter issubstantially identical to the construction of the various embodimentsof the integrating cavities. In both the object is to have optimaldiffusion of the reflected component of the cavity radiation from themultiple interlocking reflecting elements formed in the wall of thechamber. The output radiation from the cavity is then sampled orutilized after it leaves the cavity via the output aperture. Hence,although the most common embodiment for the black body emitter will bethe spherical chamber with spherical deformations forming theinterlocking reflecting elements on its interior, it is possible thatcylindrical and elliptical black body emitter chambers may also beutilized should the specific application so require.

Another embodiment is a hybrid radiation dispersing cavity which may becalled a modified grey-body source which generates part of its energythermally and obtains part from another radiation source which feedsinto it.

I claim:
 1. A cavity for the diffusion of radiation of a bandwidthhaving a maximum wavelength of about 100 microns comprising a cavitysurface substantially covered by a plurality of interlockingdeformations comprising at least two sets of deformations for producingat least two apparent planes or reflection from at least two differentsets of deformations wherein adjacent deformations have oppositeconcavities such that no sharp intersections between deformations arepresent, each deformation being a surface of revolution whose axis issubstantially normal to the cavity surface wherein the surface ofrevolution is formed by a conic such that a cross section containing theaxis is a portion of the conic subtending of arc of from 10° to about140° measured from the focus of the conic and the arc having aneffective diameter measured across the end points of the arc wherein theratio of the longest wavelength in the bandawidth to the arc diameter ofa deformation is less than one-fifth and wherein the diameter of thecavity is at least five times the arc diameter of a deformation, whereinthe cavity surface is characterized by a specific reflectivity for thebandwidth of the radiation wherein the cavity comprises an enclosedsurface having at least one aperture to serve as inlet and outletapertures such that a Lambertian distribution of radiation is producedand is accessible at the outlet aperture.
 2. A cavity for the diffusionof radiation of a bandwidth having a maximum wavelength of about 100microns comprising a cavity surface substantially covered by a pluralityof interlocking deformations comprising at least two sets ofdeformations for producing at least two apparent planes of reflectionfrom at least two different sets of deformations wherein adjacentdeformations have opposite concavities such that no sharp intersectionsbetween deformations are present, each deformation having a crosssection which is a portion of a circle subtending an arc of from about10° to about 140° measured from the center of curvature of thedeformation and the arc having a diameter measured across the end pointsof the arc wherein the ratio of the longest wavelength in the bandwidthto the arc diameter of a deformation is less than one fifth and whereinthe diameter of the cavity is at least five times the arc diameter of adeformation, wherein the cavity surface is characterized by a specificreflectivity for the bandwidth of the radiation wherein the cavitycomprises an enclosed surface having at least one aperture to serve asinlet and outlet apertures such that a Lambertian distribution ofradiation is produced and is accessible at the outlet aperture.
 3. Theradiation diffusion of claim 2 wherein the cavity is an integratingcavity.
 4. The radiation diffusion cavity of claim 2 wherein the cavityis to be used as a black body emitter through the aperture wherein thereflectivity of the surface is less than about 1.0%.
 5. An integratingcavity for mixing radiation of a bandwidth having a maximum wavelengthof about 100 microns comprising a cavity surface substantially coveredby a plurality of interlocking deformations comprising at least two setsof deformations for producing at least two apparent planes of reflectionfrom at least two different sets of deformations wherein adjacentdeformations have opposite concavities such that no sharp intersectonsbetween deformations are present, each deformation having a crosssection which is a portion of a circle subtending an arc of from about10° to about 140° measured from the center of curvature of thedeformation and a diameter measured across the end points of the arcwherein the ratio of the longest wavelength in the bandwidth to thediameter of a deformation is less than one tenth and wherein thediameter of the cavity is at least five times the diameter of adeformation, wherein the cavity surface is covered with a coating of aspecific reflectivity for the bandwidth of the radiation wherein thecavity comprises an enclosed surface having at least one aperture toserve as inlet and outlet apertures such that a Lambertian distributionof radiation is produced and is accessible at the outlet aperture. 6.The integrating cavity of claim 5 wherein the cavity is a sphericalcavity.
 7. The integrating cavity of claim 6 wherein the deformationsare spherical deformations.
 8. A spherical integrating cavity fordispersing radiation of a bandwidth having a maximum wavelength of about100 microns comprising a cavity surface substantially covered by aplurality of interlocking deformations comprising at least two sets ofdeformations for producing at least two apparent planes of reflectionfrom at least two different sets of deformations, wherein adjacentdeformations have opposite concavities such that no sharp intersectionsbetween deformations are present, each deformation having a crosssection which is a portion of circle subtending an arc of from about 10°to about 140° measured from the center of curvature of the deformationand a diameter measured across the end points of the arc wherein theratio of the longest wavelength in the bandwidth to the diameter of adeformation is less than ten and wherein the diameter of the cavity isat least five times the diameter of a deformation, wherein the cavitysurface is covered with a coating of a specific reflectivity for thebandwidth of the radiation wherein the cavity comprises an enclosedsurface having at least one aperture to serve as inlet and outletapertures such that a Lambertian distribution of radiation is producedand is accessible at the outlet aperture.
 9. The cavity of claim 8wherein the deformations are spherical deformations.
 10. The cavity ofclaim 9 wherein the deformations are configured as two sets ofinterlocking deformations, the first set consisting of concave inwardsdeformations having a first apparent plane of reflection and the secondset consisting of convex inwards deformations having a second apparentplane of reflection.
 11. The cavity of claim 9 wherein the deformationsare configured as at least two sets of interlocking deformations, atleast one set consisting of concave inwards deformations having a firstapparent plane of reflection and at least one remaining set consistingof convex inwards deformations having a second apparent plane ofreflection.
 12. The cavity ofclaim 8 wherein the arc is from about 70°to about 100°.